Characterization of the primary structure of the major silk gene, h-fibroin, across caddisfly (Trichoptera) suborders

Larvae of caddisflies (Trichoptera) produce silk to build various underwater structures allowing them to exploit a wide range of aquatic environments. The silk adheres to various substrates underwater and has high tensile strength, extensibility, and toughness and is of interest as a model for biomimetic adhesives. As a step toward understanding how the properties of underwater silk evolved in Trichoptera, we used genomic data to identify full-length sequences and characterize the primary structure of the major silk protein, h-fibroin, across the order. The h-fibroins have conserved termini and basic motif structure with high variation in repeating modules and variation in the percentage of amino acids, mainly proline. This finding might be linked to differences in mechanical properties related to the different silk usage and sets a starting point for future studies to screen and correlate amino acid motifs and other sequence features with quantifiable silk properties.

Allelic resolution of insect and spider silk genes reveals hidden genetic diversity

Arthropod silk is vital to the evolutionary success of hundreds of thousands of species. The primary proteins in silks are often encoded by long, repetitive gene sequences. Until recently, sequencing and assembling these complex gene sequences has proven intractable given their repetitive structure. Here, using high-quality long-read sequencing, we show that there is extensive variation-both in terms of length and repeat motif order-between alleles of silk genes within individual arthropods. Further, this variation exists across two deep, independent origins of silk which diverged more than 500 Mya: the insect clade containing caddisflies and butterflies and spiders. This remarkable convergence in previously overlooked patterns of allelic variation across multiple origins of silk suggests common mechanisms for the generation and maintenance of structural protein-coding genes. Future genomic efforts to connect genotypes to phenotypes should account for such allelic variation.

Highly accurate long reads are crucial for realizing the potential of biodiversity genomics

BACKGROUND

Generating the most contiguous, accurate genome assemblies given available sequencing technologies is a long-standing challenge in genome science. With the rise of long-read sequencing, assembly challenges have shifted from merely increasing contiguity to correctly assembling complex, repetitive regions of interest, ideally in a phased manner. At present, researchers largely choose between two types of long read data: longer, but less accurate sequences, or highly accurate, but shorter reads (i.e., >Q20 or 99% accurate). To better understand how these types of long-read data as well as scale of data (i.e., mean length and sequencing depth) influence genome assembly outcomes, we compared genome assemblies for a caddisfly, Hesperophylax magnus, generated with longer, but less accurate, Oxford Nanopore (ONT) R9.4.1 and highly accurate PacBio HiFi (HiFi) data. Next, we expanded this comparison to consider the influence of highly accurate long-read sequence data on genome assemblies across 6750 plant and animal genomes. For this broader comparison, we used HiFi data as a surrogate for highly accurate long-reads broadly as we could identify when they were used from GenBank metadata.

RESULTS

HiFi reads outperformed ONT reads in all assembly metrics tested for the caddisfly data set and allowed for accurate assembly of the repetitive ~ 20 Kb H-fibroin gene. Across plants and animals, genome assemblies that incorporated HiFi reads were also more contiguous. For plants, the average HiFi assembly was 501% more contiguous (mean contig N50 = 20.5 Mb) than those generated with any other long-read data (mean contig N50 = 4.1 Mb). For animals, HiFi assemblies were 226% more contiguous (mean contig N50 = 20.9 Mb) versus other long-read assemblies (mean contig N50 = 9.3 Mb). In plants, we also found limited evidence that HiFi may offer a unique solution for overcoming genomic complexity that scales with assembly size.

CONCLUSIONS

Highly accurate long-reads generated with HiFi or analogous technologies represent a key tool for maximizing genome assembly quality for a wide swath of plants and animals. This finding is particularly important when resources only allow for one type of sequencing data to be generated. Ultimately, to realize the promise of biodiversity genomics, we call for greater uptake of highly accurate long-reads in future studies.

Material characterization of GPX®: A versatile in situ solidifying embolic platform technology

Endovascular embolization is a minimally invasive procedure during which blood flow to targeted tissues is selectively occluded. The list of clinical indications for embolization continues to expand. Liquid embolic agents are injectable compositions that transition into a solid or semi-solid form when introduced into blood vessels. The mechanism that triggers the liquid-to-solid transition is a key distinguishing feature of liquid embolic agents. GPX is a waterborne liquid embolic agent comprising oppositely charged polyelectrolytes: polyguanidinum and inorganic polyphoshate. In situ solidification is driven by electrostatic condensation of the polyelectrolytes, triggered by ionic strength differentials. We report in vitro characterization of the material properties of GPX, it is in vivo effectiveness in acute animal studies, and its potential for chemoembolization. The viscosity of GPX can be varied over a wide range by adjusting the polyguanidinium MW and/or concentration. Formulation of GPX with either tantalum microparticles (30 wt%) or iodinated radiocontrast agents (300 mgI ml^-1) did not significantly change the flow behavior of GPX; the viscosity was independent of shear rate and remained within a clinically practical range (80-160 cP). Formulation of GPX with doxorubicin substantially increased viscosity at low shear rates and resulted in a power law dependence on shear rate. High contrast and effective vascular occlusion were demonstrated in both swine kidneys and rete mirabile. Contrast from iodinated compounds was temporary, dissipating within hours. The doxorubicin in vitro release profile was linear over 90 days. The results demonstrate that GPX is a versatile liquid embolic platform that can be formulated with a wide range of viscosities injectable at clinically practical flow rates, with either transient or permanent contrast, and that can provide prolonged zero-order delivery of doxorubicin to embolized tissues.

COVID-19 ethnic inequalities in mental health and multimorbidities: protocol for the COVEIMM study

PURPOSE

The COVID-19 pandemic may have exacerbated ethnic health inequalities, particularly in people with multiple long-term health conditions, the interplay with mental health is unclear. This study investigates the impact of the pandemic on the association of ethnicity and multimorbidity with mortality/service use among adults, in people living with severe mental illnesses (SMI).

METHODS

This study will utilise secondary mental healthcare records via the Clinical Record Interactive Search (CRIS) and nationally representative primary care records through the Clinical Practice Interactive Research Database (CPRD). Quasi-experimental designs will be employed to quantify the impact of COVID-19 on mental health service use and excess mortality by ethnicity, in people living with severe mental health conditions. Up to 50 qualitative interviews will also be conducted, co-produced with peer researchers; findings will be synthesised with quantitative insights to provide in-depth understanding of observed associations.

RESULTS

81,483 people in CRIS with schizophrenia spectrum, bipolar or affective disorder diagnoses, were alive from 1st January 2019. Psychiatric multimorbidities in the CRIS sample were comorbid somatoform disorders (30%), substance use disorders (14%) and personality disorders (12%). In CPRD, of 678,842 individuals with a prior probable diagnosis of COVID-19, 1.1% (N = 7493) had an SMI diagnosis. People in the SMI group were more likely to die (9% versus 2% in the non-SMI sample) and were more likely to have mental and physical multimorbidities.

CONCLUSION

The effect of COVID-19 on people from minority ethnic backgrounds with SMI and multimorbidities remains under-studied. The present mixed methods study aims to address this gap.

Conservation of Three-Dimensional Structure of Lepidoptera and Trichoptera L-Fibroins for 290 Million Years

The divergence of sister orders Trichoptera (caddisflies) and Lepidoptera (moths and butterflies) from a silk-spinning ancestor occurred around 290 million years ago. Trichoptera larvae are mainly aquatic, and Lepidoptera larvae are almost entirely terrestrial—distinct habitats that required molecular adaptation of their silk for deployment in water and air, respectively. The major protein components of their silks are heavy chain and light chain fibroins. In an effort to identify molecular changes in L-fibroins that may have contributed to the divergent use of silk in water and air, we used the ColabFold implementation of AlphaFold2 to predict three-dimensional structures of L-fibroins from both orders. A comparison of the structures revealed that despite the ancient divergence, profoundly different habitats, and low sequence conservation, a novel 10-helix core structure was strongly conserved in L-fibroins from both orders. Previously known intra- and intermolecular disulfide linkages were accurately predicted. Structural variations outside of the core may represent molecular changes that contributed to the evolution of insect silks adapted to water or air. The distributions of electrostatic potential, for example, were not conserved and present distinct order-specific surfaces for potential interactions with or modulation by external factors. Additionally, the interactions of L-fibroins with the H-fibroin C-termini are different for these orders; lepidopteran L-fibroins have N-terminal insertions that are not present in trichopteran L-fibroins, which form an unstructured ribbon in isolation but become part of an intermolecular β-sheet when folded with their corresponding H-fibroin C-termini. The results are an example of protein structure prediction from deep sequence data of understudied proteins made possible by AlphaFold2.

1017 Early Mobilisation After Stable Distal Radius Fracture – an Audit of BOAST Guideline Adherence

Aim

Distal radius (DR) fractures are among the commonest fractures seen by orthopaedics. The management of these fractures is dependent on the stability of the fracture, and conservative management is usually favoured for stable fractures. Mobilisation of the wrist following this stable fracture is necessary to avoid the risks of wrist stiffness, complex regional pain syndrome and limitation of function. According to BOAST guidelines for management of DR fractures: patients with a stable fracture should be considered for early mobilisation with a removable support once pain allows. The aim of this study was to determine our unit's adherence to guidelines and review the period of immobilisation of stable DR fractures.

Method

Retrospective analysis of virtual fracture clinic referrals, ED and clinic notes, imaging and any further correspondence of patients referred to our orthopaedic team between 1/2/20–30/7/20 with isolated DR fracture.

Results

Of 163 patients referred with DR fracture, 49.7% were deemed to have a stable fracture. Of these patients, only 37% were mobilised early, with the remainder fully immobilised for 6 weeks without active mobilisation protocol.

Conclusions

A large proportion of patients with stable fractures are not being managed in accordance with BOAST guidelines, therefore a standardised intervention is needed to ensure patients regain maximum possible function. We propose that a new protocol is put in place to screen all DR fractures within our virtual fracture clinic into stable v. unstable pattern and if deemed stable to ensure patient is seen for early physiotherapy face to face or virtually.

Long-read HiFi sequencing correctly assembles repetitive heavy fibroin silk genes in new moth and caddisfly genomes

Insect silk is a versatile biomaterial. Lepidoptera and Trichoptera display some of the most diverse uses of silk, with varying strength, adhesive qualities, and elastic properties. Silk fibroin genes are long (>20 Kbp), with many repetitive motifs that make them challenging to sequence. Most research thus far has focused on conserved N- and C-terminal regions of fibroin genes because a full comparison of repetitive regions across taxa has not been possible. Using the PacBio Sequel II system and SMRT sequencing, we generated high fidelity (HiFi) long-read genomic and transcriptomic sequences for the Indianmeal moth (Plodia interpunctella) and genomic sequences for the caddisfly Eubasilissa regina. Both genomes were highly contiguous (N50  = 9.7 Mbp/32.4 Mbp, L50  = 13/11) and complete (BUSCO complete  = 99.3%/95.2%), with complete and contiguous recovery of silk heavy fibroin gene sequences. We show that HiFi long-read sequencing is helpful for understanding genes with long, repetitive regions.

Genome size evolution in the diverse insect order Trichoptera

Background

Genome size is implicated in the form, function, and ecological success of a species. Two principally different mechanisms are proposed as major drivers of eukaryotic genome evolution and diversity: polyploidy (i.e., whole-genome duplication) or smaller duplication events and bursts in the activity of repetitive elements. Here, we generated de novo genome assemblies of 17 caddisflies covering all major lineages of Trichoptera. Using these and previously sequenced genomes, we use caddisflies as a model for understanding genome size evolution in diverse insect lineages.

Results

We detect a ∼14-fold variation in genome size across the order Trichoptera. We find strong evidence that repetitive element expansions, particularly those of transposable elements (TEs), are important drivers of large caddisfly genome sizes. Using an innovative method to examine TEs associated with universal single-copy orthologs (i.e., BUSCO genes), we find that TE expansions have a major impact on protein-coding gene regions, with TE-gene associations showing a linear relationship with increasing genome size. Intriguingly, we find that expanded genomes preferentially evolved in caddisfly clades with a higher ecological diversity (i.e., various feeding modes, diversification in variable, less stable environments).

Conclusion

Our findings provide a platform to test hypotheses about the potential evolutionary roles of TE activity and TE-gene associations, particularly in groups with high species, ecological, and functional diversities.

Rapid Entrapment of Phenazine Ethosulfate within a Polyelectrolyte Complex on Electrodes for Efficient NAD+ Regeneration in Mediated NAD+-Dependent Bioelectrocatalysis

Over the past two decades, the designs of redox polymers have become critical to the field of mediated bioelectrocatalysis and are used in commercial glucose biosensors, as well as other bioelectrochemical applications (e.g., energy harvesting). These polymers are specifically used to immobilize redox mediators on electrode surfaces, allowing for self-exchange-based conduction of electrons from enzymes far from the electrode to the electrode surface. However, the synthesis of redox polymers is challenging and results in large batch-to-batch variability. Herein, we report a rapid entrapment of mediators for NAD⁺-dependent bioelectrocatalysis within reverse ionically condensed polyelectrolytes. A high ionic strength aqueous solution of oppositely charged polyelectrolytes, composed of cationic polyguanidinium (PG) chloride and anionic sodium hexametaphosphate (P6), undergoes phase inversion into a solid microporous polyelectrolyte complex (PEC) when introduced into a low ionic strength aqueous solution. The ionic strength-triggered phase inversion of PGP6 solutions was investigated as a means to entrap mediators on the surface of electrodes for mediated bioelectrocatalysis. Compared to the traditional cross-linked immobilizations using redox polymers, this phase inversion takes place within seconds and requires up to 60 min for complete stabilization. In this work, redox mediator phenazine ethosulfate (PES) was entrapped within PGP6 on electrode surfaces for nicotinamide adenine dinucleotide (NAD⁺)-dependent bioelectrocatalysis. In the bulk solution, NAD⁺-dependent dehydrogenase enzymes catalyze the oxidation of the substrate while reducing NAD to reduced nicotinamide adenine dinucleotide (NADH). The resulting NADH is reoxidized to NAD⁺ by the entrapped PES that gets reduced on the electrode, completing the NAD⁺-regeneration-based bioelectrocatalysis. To show the use of these new materials in an application, biofuel cells were evaluated using four different anodic enzyme systems (alcohol dehydrogenase, lactate hydrogenase, glycerol dehydrogenase, and glucose dehydrogenase).

Draft Genome Assemblies and Annotations of Agrypnia vestita Walker, and Hesperophylax magnus Banks Reveal Substantial Repetitive Element Expansion in Tube Case-Making Caddisflies (Insecta: Trichoptera)

Trichoptera (caddisflies) play an essential role in freshwater ecosystems; for instance, larvae process organic material from the water and are food for a variety of predators. Knowledge on the genomic diversity of caddisflies can facilitate comparative and phylogenetic studies thereby allowing scientists to better understand the evolutionary history of caddisflies. Although Trichoptera are the most diverse aquatic insect order, they remain poorly represented in terms of genomic resources. To date, all long-read based genomes have been sequenced from individuals in the retreat-making suborder, Annulipalpia, leaving ∼275 Ma of evolution without high-quality genomic resources. Here, we report the first long-read based de novo genome assemblies of two tube case-making Trichoptera from the suborder Integripalpia, Agrypnia vestita Walker and Hesperophylax magnus Banks. We find that these tube case-making caddisflies have genome sizes that are at least 3-fold larger than those of currently sequenced annulipalpian genomes and that this pattern is at least partly driven by major expansion of repetitive elements. In H. magnus, long interspersed nuclear elements alone exceed the entire genome size of some annulipalpian counterparts suggesting that caddisflies have high potential as a model for understanding genome size evolution in diverse insect lineages.

Trends in the delivery of elective general paediatric surgery

INTRODUCTION

There has been regular dialogue regarding the importance of developing clinical networks to compensate for the steady decline in general paediatric surgery performed by adult surgeons. Despite this dialogue, there are no contemporary published data to quantify the issue. This report documents patterns in delivery of general paediatric surgery in England and shows what is being performed where and by whom.

MATERIALS AND METHODS

Using the Surgical Workload Outcome Database, we compared hospital-level data between 2009 and 2017. Inclusion criteria were children under 18 years admitted to NHS hospitals in England for elective general paediatric surgery. Data were analysed with an online statistical package performing paired t-tests.

RESULTS

There was no real change in the overall number of elective general paediatric surgical marker cases, but the type mix has changed. The number of marker cases performed by adult surgeons fell by 34% (4699 vs 3090 p < 0.05). The number of marker cases performed by specialist paediatric surgeons increased by 21% (8184 vs 9862 p < 0.05). This increase in workload occurred in both tertiary (21% increase) and peripheral (18% increase) centres. When analysing data by operation type it was apparent that 78% of the increased workload was attributable to an increase in orchidopexy rate.

CONCLUSION

Best practice is to treat children close to home by staff with the right skills. This study shows significant shifts in the general paediatric surgical workload. It is important to monitor these trends for successful succession planning as well as configuration of services.

Direct bioelectrocatalysis by redox enzymes immobilized in electrostatically condensed oppositely charged polyelectrolyte electrode coatings

The ionic induced phase inversion of two oppositely charged electrolytes for enzyme immobilization and its application in bioelectrocatalysis.

Annotated Draft Genomes of Two Caddisfly Species Plectrocnemia conspersa CURTIS and Hydropsyche tenuis NAVAS (Insecta: Trichoptera)

Members of the speciose insect order Trichoptera (caddisflies) provide important ecosystem services, for example, nutrient cycling through breaking down of organic matter. They are also of industrial interest due to their larval silk secretions. These form the basis for their diverse case-making behavior that allows them to exploit a wide range of ecological niches. Only five genomes of this order have been published thus far, with variable qualities regarding contiguity and completeness. A low-cost sequencing strategy, that is, using a single Oxford Nanopore flow cell per individual along with Illumina sequence reads was successfully used to generate high-quality genomes of two Trichoptera species, Plectrocnemia conspersa and Hydropsyche tenuis. Of the de novo assembly methods compared, assembly of low coverage Nanopore reads (∼18×) and subsequent polishing with long reads followed by Illumina short reads (∼80-170× coverage) yielded the highest genome quality both in terms of contiguity and BUSCO completeness. The presented genomes are the shortest to date and extend our knowledge of genome size across caddisfly families. The genomic region that encodes for light (L)-chain fibroin, a protein component of larval caddisfly silk was identified and compared with existing L-fibroin gene clusters. The new genomic resources presented in this paper are among the highest quality Trichoptera genomes and will increase the knowledge of this important insect order by serving as the basis for phylogenomic and comparative genomic studies.

Exploring the underwater silken architectures of caddisworms: comparative silkomics across two caddisfly suborders

Caddisfly (Trichoptera) larvae assemble a variety of underwater structures using bioadhesive silk. The order is divided into two primary sub-orders distinguished by how the larvae deploy their silk. Foraging Integripalpia larvae construct portable tube cases. Annulipalpia larvae construct stationary retreats, some with suspended nets to capture food. To identify silk molecular adaptations that may have contributed to caddisfly diversification, we report initial characterization of silk from a net-spinner genus, Parapsyche, for comparison with the silk of a tube case-maker genus, Hesperophylax. Overall, general features of silk structure and processing are conserved across the sub-orders despite approximately 200 Ma of divergence: the H-fibroin proteins comprise repeating phosphoserine-rich motifs, naturally spun silk fibres contain approximately 1 : 1 molar ratios of divalent metal ions to phosphate, silk fibre precursors are stored as complex fluids of at least two types of complexes, and silk gland proteins contain only traces of divalent metal ions, suggesting metal ions that solidify the fibres are absorbed from the aqueous environment after silk extrusion. However, the number and arrangement of the repeating phosphoserine blocks differ between genera, suggesting molecular adaptation of H-fibroin through duplication and shuffling of conserved structural modules may correspond with the radiation of caddisflies into diverse environments. This article is part of the theme issue 'Transdisciplinary approaches to the study of adhesion and adhesives in biological systems'.

Aqueous Liquid-Liquid Phase Separation of Natural and Synthetic Polyguanidiniums

Protamines are natural polyguanidiniums, arginine(R)-rich proteins involved in the compaction of chromatin during vertebrate spermatogenesis. Salmine, a protamine isolated from salmon sperm, contains 65 mol% R residues, with positively charged guanidino (Gdm⁺) sidechains, and no other amino acids with ionizable or aromatic sidechains. Salmine sulfate solutions undergo liquid-liquid phase separation (LLPS) with a concentration-dependent upper critical solution temperature (UCST). The condensed liquid phase comprises 50 wt % water and >600 mg·mL⁻¹ salmine with a constant 1:2 ratio of sulfate (SO₄²⁻) to Gdm⁺. Isothermal titration calorimetry, titrating Na₂SO₄ into salmine chloride above and below the UCST, allowed isolation of exothermic sulfate binding to salmine chloride from subsequent endothermic condensation and exothermic phase separation events. Synthetic random polyacrylate analogs of salmine, with 3-guanidinopropyl sidechains, displayed similar counterion dependent phase behavior, demonstrating that the LLPS of polyguanidiniums does not depend upon subunit sequence or polymer backbone chirality, and was due entirely to Gdm⁺ sidechain interactions. The results provide experimental evidence for like-charge pairing of Gdm⁺ sidechains, and an experimental approach for further characterizing these interactions.

The genome of an underwater architect, the caddisfly Stenopsyche tienmushanensis Hwang (Insecta: Trichoptera)

Background

Caddisflies (Insecta: Trichoptera) are a highly adapted freshwater group of insects split from a common ancestor with Lepidoptera. They are the most diverse (>16,000 species) of the strictly aquatic insect orders and are widely employed as bio-indicators in water quality assessment and monitoring. Among the numerous adaptations to aquatic habitats, caddisfly larvae use silk and materials from the environment (e.g., stones, sticks, leaf matter) to build composite structures such as fixed retreats and portable cases. Understanding how caddisflies have adapted to aquatic habitats will help explain the evolution and subsequent diversification of the group.

Findings

We sequenced a retreat-builder caddisfly Stenopsyche tienmushanensis Hwang and assembled a high-quality genome from both Illumina and Pacific Biosciences (PacBio) sequencing. In total, 601.2 M Illumina reads (90.2 Gb) and 16.9 M PacBio subreads (89.0 Gb) were generated. The 451.5 Mb assembled genome has a contig N50 of 1.29 M, has a longest contig of 4.76 Mb, and covers 97.65% of the 1,658 insect single-copy genes as assessed by Benchmarking Universal Single-Copy Orthologs. The genome comprises 36.76% repetitive elements. A total of 14,672 predicted protein-coding genes were identified. The genome revealed gene expansions in specific groups of the cytochrome P450 family and olfactory binding proteins, suggesting potential genomic features associated with pollutant tolerance and mate finding. In addition, the complete gene complex of the highly repetitive H-fibroin, the major protein component of caddisfly larval silk, was assembled.

Conclusions

We report the draft genome of Stenopsyche tienmushanensis, the highest-quality caddisfly genome so far. The genome information will be an important resource for the study of caddisflies and may shed light on the evolution of aquatic insects.

Deep-learning-assisted diagnosis for knee magnetic resonance imaging: Development and retrospective validation of MRNet

BACKGROUND

Magnetic resonance imaging (MRI) of the knee is the preferred method for diagnosing knee injuries. However, interpretation of knee MRI is time-intensive and subject to diagnostic error and variability. An automated system for interpreting knee MRI could prioritize high-risk patients and assist clinicians in making diagnoses. Deep learning methods, in being able to automatically learn layers of features, are well suited for modeling the complex relationships between medical images and their interpretations. In this study we developed a deep learning model for detecting general abnormalities and specific diagnoses (anterior cruciate ligament [ACL] tears and meniscal tears) on knee MRI exams. We then measured the effect of providing the model's predictions to clinical experts during interpretation.

METHODS AND FINDINGS

Our dataset consisted of 1,370 knee MRI exams performed at Stanford University Medical Center between January 1, 2001, and December 31, 2012 (mean age 38.0 years; 569 [41.5%] female patients). The majority vote of 3 musculoskeletal radiologists established reference standard labels on an internal validation set of 120 exams. We developed MRNet, a convolutional neural network for classifying MRI series and combined predictions from 3 series per exam using logistic regression. In detecting abnormalities, ACL tears, and meniscal tears, this model achieved area under the receiver operating characteristic curve (AUC) values of 0.937 (95% CI 0.895, 0.980), 0.965 (95% CI 0.938, 0.993), and 0.847 (95% CI 0.780, 0.914), respectively, on the internal validation set. We also obtained a public dataset of 917 exams with sagittal T1-weighted series and labels for ACL injury from Clinical Hospital Centre Rijeka, Croatia. On the external validation set of 183 exams, the MRNet trained on Stanford sagittal T2-weighted series achieved an AUC of 0.824 (95% CI 0.757, 0.892) in the detection of ACL injuries with no additional training, while an MRNet trained on the rest of the external data achieved an AUC of 0.911 (95% CI 0.864, 0.958). We additionally measured the specificity, sensitivity, and accuracy of 9 clinical experts (7 board-certified general radiologists and 2 orthopedic surgeons) on the internal validation set both with and without model assistance. Using a 2-sided Pearson's chi-squared test with adjustment for multiple comparisons, we found no significant differences between the performance of the model and that of unassisted general radiologists in detecting abnormalities. General radiologists achieved significantly higher sensitivity in detecting ACL tears (p-value = 0.002; q-value = 0.019) and significantly higher specificity in detecting meniscal tears (p-value = 0.003; q-value = 0.019). Using a 1-tailed t test on the change in performance metrics, we found that providing model predictions significantly increased clinical experts' specificity in identifying ACL tears (p-value < 0.001; q-value = 0.006). The primary limitations of our study include lack of surgical ground truth and the small size of the panel of clinical experts.

CONCLUSIONS

Our deep learning model can rapidly generate accurate clinical pathology classifications of knee MRI exams from both internal and external datasets. Moreover, our results support the assertion that deep learning models can improve the performance of clinical experts during medical imaging interpretation. Further research is needed to validate the model prospectively and to determine its utility in the clinical setting.

Aquatic caddisworm silk is solidified by environmental metal ions during the natural fiber-spinning process

Aquatic caddisfly larvae (caddisworms) wet-spin fibers to construct composite cases of silk and stone. The silk emerges from labial ducts as a nanofibrous fluid gel, flowing over the stone substrate and making intimate interfacial adhesive contacts before being drawn into tough fibers that rapidly solidify underwater to span gaps in the construction. Divalent metal ions are responsible for the unique mechanical properties of naturally spun silk fibers; however, when and where divalent metal ions are incorporated into the metallofibers and other aspects of the fiber solidification mechanism are poorly understood. To investigate, the elemental composition and secondary structure of silk precursors stored in the silk gland lumen were compared with naturally spun fibers by inductively coupled plasma optical emission spectroscopy and attenuated total reflection Fourier transform infrared spectroscopy. Naturally spun fibers contained near equimolar ratios of Ca²⁺ to P. In contrast, silk precursors stored in the silk gland lumen contained only traces of Ca²⁺ and other multivalent metal ions. Ca²⁺ was also undetectable in anterior lumenal silk using the histochemical Ca²⁺ indicator, alizarin S red. Addition of Ca²⁺ to isolated lumenal silk resulted in Ca²⁺ complexation by H-fibroin phosphoserines (pSs) and a shift in secondary structure from random coils to β-structures, creating infrared spectra in the phosphate and amide I regions nearly equivalent to those found in naturally spun Ca²⁺-containing silk fibers. Light and electron microscopy within distinct regions of the silk gland suggested that posterior gland silk colloidal complexes transition into a nanofibrous morphology as they pass into the chitin-lined anterior lumen. Altogether, the results suggest that environmental Ca²⁺ absorbed from natural water triggers silk fiber solidification postdraw by complexing H-fibroin pSs, creating Ca²⁺-stabilized crystalline β-nanodomains that cross-link and toughen the freshly drawn silk fibers.-Ashton, N. N., Stewart, R. J. Aquatic caddisworm silk is solidified by environmental metal ions during the natural fiber-spinning process.

Complex coacervation

Guest editors Paul Dubin and Russell J. Stewart introduce this Soft Matter themed collection on complex coacervation.

Complex coacervation of Mg(ii) phospho-polymethacrylate, a synthetic analog of sandcastle worm adhesive phosphoproteins

The highly phosphorylated Pc3 proteins, major components of the sandcastle worm adhesive, are sequestered with Mg as spherical sub-granules within heterogeneous secretory granules in adhesive gland cells. The phase behavior of a synthetic phospho-polymethacrylate analog of the Pc3 phosphoproteins, in the presense of Mg(ii), was characterized to determine whether it is chemically possible for the natural adhesive components to be packaged and stored as liquid complex coacervates. Of several multivalent metal salts tested, only MgCl induced complex coacervation of the phospho-copolymer. Complex coacervates formed at Mg/P ratios from 0.5-8, and in [NaCl]s from 0-3 M. At low temperature and pH, the complex coacervates were clear and homogeneous. At higher temperatures and pH, the coacervate phases were translucent. The elastic and viscous moduli initially decreased as temperature increased, but then increased significantly near the temperature boundary between clear and translucent forms. A mechanism is proposed in which relatively weak, ionic strength-independent, outer shell crossbridging of -PO₃^2- sidechains by Mg[H₂O]₆²⁺ complex ions is responsible for the clear homogeneous lower viscosity coacervate form. At higher temperature and pH, displacement of inner shell H₂O molecules by phosphate O^- ligands creates stronger crossbridges, additional dehydration, and more viscous coacervates. The results demonstrate that Pc3 phosphoproteins can exist as condensed phospho/Mg(ii) complex coacervates under conditions expected in the adhesive glands of sandcastle worms in their natural environment. Considering the common regulatory role of phosphorylation and the intracellular abundance of Mg²⁺ it is possible that soft bridging of phosphate groups by Mg[H₂O]_n²⁺ may promote other regulated cellular liquid liquid phase separation phenomena.

Do animal exhibitors support and follow recommendations to prevent transmission of variant influenza at agricultural fairs? A survey of animal exhibitor households after a variant influenza virus outbreak in Michigan

Influenza A viruses circulate in swine and can spread rapidly among swine when housed in close proximity, such as at agricultural fairs. Youth who have close and prolonged contact with influenza-infected swine at agricultural fairs may be at increased risk of acquiring influenza virus infection from swine. Animal and human health officials have issued written measures to minimize influenza transmission at agricultural exhibitions; however, there is little information on the knowledge, attitudes, and practice (KAP) of these measures among animal exhibitors. After an August 2016 outbreak of influenza A(H3N2) variant (“H3N2v”) virus infections (i.e., humans infected with swine influenza viruses) in Michigan, we surveyed households of animal exhibitors at eight fairs (including one with known H3N2v infections) to assess their KAP related to variant virus infections and their support for prevention measures. Among 170 households interviewed, most (90%, 151/167) perceived their risk of acquiring influenza from swine to be low or very low. Animal exhibitor households reported high levels of behaviours that put them at increased risk of variant influenza virus infections, including eating or drinking in swine barns (43%, 66/154) and hugging, kissing or snuggling with swine at agricultural fairs (31%, 48/157). Among several recommendations, including limiting the duration of swine exhibits and restricting eating and drinking in the animal barns, the only recommendation supported by a majority of households was the presence of prominent hand-washing stations with a person to monitor hand-washing behaviour (76%, 129/170). This is a unique study of KAP among animal exhibitors and highlights that animal exhibitor households engage in behaviours that could increase their risk of variant virus infections and have low support for currently recommended measures to minimize infection transmission. Further efforts are needed to understand the lack of support for recommended measures and to encourage healthy behaviours at fairs.

The role of coacervation and phase transitions in the sandcastle worm adhesive system

Sandcastle worms, Phragmatopoma californica (Fewkes), live along the western coast of North America. Individual worms build tubular shells under seawater by gluing together sandgrains and biomineral particles with a multipart, rapid-set, self-initiating adhesive. The glue comprises distinct sets of condensed, oppositely charged polyelectrolytic components-polyphosphates, polysulfates, and polyamines-that are separately granulated and stored at high concentration in distinct cell types. The pre-organized adhesive modules are secreted separately and intact, but rapidly fuse with minimal mixing and expand into a crack-penetrating complex fluid. Within 30s of secretion into seawater, the fluid adhesive transitions (sets) into a porous solid adhesive joint. The nano- and microporous structure of the foamy solid adhesive contributes to the strength and toughness of the adhesive joint through several mechanisms. A curing agent (catechol oxidase), co-packaged into both types of adhesive granules, covalently cross-links the adhesive and becomes a structural component of the final adhesive joint. The overall effectiveness of the granulated sandcastle glue is more a product of the cellular sorting and packaging mechanisms, the transition from fluid to solid following secretion, and its final biphasic porous structure as it is of its composition or any particular amino acid modification.

Peroxidase-catalysed interfacial adhesion of aquatic caddisworm silk

Casemaker caddisfly (Hesperophylax occidentalis) larvae use adhesive silk fibres to construct protective shelters under water. The silk comprises a distinct peripheral coating on a viscoelastic fibre core. Caddisworm silk peroxinectin (csPxt), a haem-peroxidase, was shown to be glycosylated by lectin affinity chromatography and tandem mass spectrometry. Using high-resolution H2O2 and peroxidase-dependent silver ion reduction and nanoparticle deposition, imaged by electron microscopy, csPxt activity was shown to be localized in the peripheral layer of drawn silk fibres. CsPxt catalyses dityrosine cross-linking within the adhesive peripheral layer post-draw, initiated perhaps by H2O2 generated by a silk gland-specific superoxide dismutase 3 (csSOD3) from environmental reactive oxygen species present in natural water. CsSOD3 was also shown to be a glycoprotein and is likely localized in the peripheral layer. Using a synthetic fluorescent phenolic copolymer and confocal microscopy, it was shown that csPxt catalyses oxidative cross-linking to external polyphenolic compounds capable of diffusive interpenetration into the fuzzy peripheral coating, including humic acid, a natural surface-active polyphenol. The results provide evidence of enzyme-mediated covalent cross-linking of a natural bioadhesive to polyphenol conditioned interfaces as a mechanism of permanent adhesion underwater.

Connecting caddisworm silk structure and mechanical properties: combined infrared spectroscopy and mechanical analysis

The underwater silk of an aquatic casemaking caddisfly larvae (Hesperophylax occidentalis) is viscoelastic, and displays distinct yield behaviour, large strain cycle hysteresis and near complete recovery of its initial strength and stiffness when unloaded. Yield followed by a stress plateau has been attributed to sequential rupture of serial Ca(2+)-cross-linked phosphoserine (pS) β-domains. Spontaneous recovery has been attributed to refolding of the Ca(2+)/pS domains powered by an elastic network. In this study, native Ca(2+) ions were exchanged with other metal ions, followed by combined mechanical and FTIR analysis to probe the contribution of pS/metal ion complexes to silk mechanical properties. After exchange of Ca(2+) with Na(+), the fibres are soft elastomers and the infrared spectra are consistent with Cv3 symmetry of the -[Formula: see text] groups. Multivalent metal ions decreased the -[Formula: see text] symmetry and the symmetric stretching modes (vs) split in a manner characteristic of ordered phosphate compounds, such as phosphate minerals and lamellar bilayers of phosphatidic acid lipids. Integrated intensities of the vs bands, indicative of the metal ion's effect on transition dipole moment of the P-O bonds, and thereby the strength of the phosphate metal complex, increased in the order: Na(+) < Mg(2+) < Sr(2+) < Ba(2+) < Ca(2+) < Eu(3+) < La(3+) < Zn(2+) < Fe(2+) With a subset of the metal ion series, the initial stiffness and yield stress of metal ion-exchanged fibres increased in the same order: [Formula: see text] [Formula: see text] establishing the link between phosphate transition dipole moments and silk fibre strength.

Water-Borne Endovascular Embolics Inspired by the Undersea Adhesive of Marine Sandcastle Worms

Transcatheter embolization is used to treat vascular malformations and defects, to control bleeding, and to selectively block blood supply to tissues. Liquid embolics are used for small vessel embolization that require distal penetration. Current liquid embolic agents have serious drawbacks, mostly centered around poor handling characteristics and toxicity. In this work, a water-borne in situ setting liquid embolic agent is described that is based on electrostatically condensed, oppositely charged polyelectrolytes-complex coacervates. At high ionic strengths, the embolic coacervates are injectable fluids that can be delivered through long narrow microcatheters. At physiological ionic strength, the embolic coacervates transition into a nonflowing solid morphology. Transcatheter embolization of rabbit renal arteries demonstrated capillary level penetration, homogeneous occlusion, and 100% devascularization of the kidney, without the embolic crossing into venous circulation. The benign water-borne composition and setting mechanism avoids many of the problems of current liquid embolics, and provides precise temporal and spatial control during endovascular embolization.

Cryopreserved human umbilical cord patch for in-utero spina bifida repair

OBJECTIVE

To identify a patch system to repair surgically created spina bifida in a sheep model for its efficacy in healing the skin defect, protecting the underlying spinal cord and reducing the Chiari II malformation.

METHODS

Spina bifida was created surgically in 16 fetuses from eight timed-pregnant sheep at gestational age of 75 days. Two fetuses did not survive the procedure. Repeat hysterotomy was performed at 95 days' gestation to cover the defect with either biocellulose film with underwater adhesive (BCF-adhesive) (n = 7) or human umbilical cord with suture (HUC-suture) (n = 7). Three fetuses without formation of the defect served as reference controls. The skin healing was examined by direct visualization after a planned Cesarean section at term, followed by histological analysis using hematoxylin and eosin and Masson's trichrome stains. Mid-sagittal sections of the fetal cranium and upper cervical spine were analyzed by a pediatric neuroradiologist who was blinded to the type of patch received.

RESULTS

Three fetuses that received the BCF-adhesive and six fetuses that received the HUC-suture survived to term for final analysis. As a result of dislodgment of the BCF-adhesive, all spina bifida defects repaired using BCF-adhesive were not healed and showed exposed spinal cord with leakage of cerebrospinal fluid. In contrast, all spinal defects repaired by HUC-suture were healed with complete regrowth of epidermal, dermal and subdermal tissue components, with no exposed spinal cord. The maximal skin wound width was 21 ± 3.6 mm in the BCF-adhesive group but 3 ± 0.8 mm in the HUC-suture group (P < 0.001). The spinal cord area (P = 0.001) and the number of anterior horn cells (P = 0.03) was preserved to a greater degree in the HUC-suture group than in the BCF-adhesive group, whilst psammoma bodies, signifying neuronal degeneration, were only observed in the BCF-adhesive group. Anatomic changes, indicative of Chiari II malformation, were seen in all three fetuses of the BCF-adhesive group but in none of the HUC-suture group (P < 0.01).

CONCLUSION

Cryopreserved umbilical cord graft is a promising regenerative patch for intrauterine repair of spina bifida.

Toughened hydrogels inspired by aquatic caddisworm silk

Aquatic caddisworm silk is a tough adhesive fiber. Part of the toughening mechanism resides in serial, Ca(2+)-phosphate crosslinked nano-domains that comprise H-fibroin, the major structural protein. To mimic the toughening mechanism, a synthetic phosphate-graft-methacrylate prepolymer, as a simple H-fibroin analog, was copolymerized within a covalent elastic network of polyacrylamide. Above a critical phosphate sidechain density, hydrogels equilibrated with Ca(2+) or Zn(2+) ions displayed greatly increased initial stiffness, strain-rate dependent yield behavior, and required 100 times more work to fracture than hydrogels equilibrated with Mg(2+) or Na(+) ions. Conceptually, the enhanced toughness is attributed to energy-dissipating, viscous unfolding of clustered phosphate-metal ion crosslinks at a critical stress. The toughness of the bioinspired hydrogels exceeds the toughness of cartilage and meniscus suggesting potential application as prosthetic biomaterials. The tough hydrogels also provide a simplified model to test hypotheses about caddisworm silk architecture, phosphate metal ion interactions, and mechanochemical toughening mechanisms.

Cryopreserved human amniotic membrane and a bioinspired underwater adhesive to seal and promote healing of iatrogenic fetal membrane defect sites

INTRODUCTION

We investigated the ability of cryopreserved human amniotic membrane (hAM) scaffold sealed with an underwater adhesive, bio-inspired by marine sandcastle worms to promote healing of iatrogenic fetal membrane defects in a pregnant swine model.

METHODS

Twelve Yucatan miniature pigs underwent laparotomy under general anesthesia at 70 days gestation (term = 114 days). The gestational sacs were assigned to uninstrumented (n = 24) and instrumented with 12 Fr trocar, which was further randomized into four different arms-no hAM patch, (n = 22), hAM patch secured with suture (n = 16), hAM patch with no suture (n = 14), and hAM patch secured with adhesive (n = 9). The animals were euthanized 20 days after the procedure. Gross and histological examination of the entry site was performed for fetal membrane healing.

RESULTS

There were no differences in fetal survival, amniotic fluid levels, or dye-leakage from the amniotic cavity between the groups. The fetal membranes spontaneously healed in instrumented sacs without hAM patches. In sacs with hAM patches secured with sutures, the patch was incorporated into the swine fetal membranes. In sacs with hAM patches without sutures, 100% of the patches were displaced from the defect site, whereas in sacs with hAM patches secured with adhesive 55% of the patches remained in place and showed complete healing (p = 0.04).

DISCUSSION

In contrast to humans, swine fetal membranes heal spontaneously after an iatrogenic injury and thus not an adequate model. hAM patches became incorporated into the defect site by cellular ingrowth from the fetal membranes. The bioinspired adhesive adhered the hAM patches within the defect site.

Self-recovering caddisfly silk: energy dissipating, Ca(2+)-dependent, double dynamic network fibers

Single fibers of the sticky underwater larval silk of the casemaker caddisfly (H. occidentalis) are viscoelastic, display large strain cycle hysteresis, and self-recover 99% of their initial stiffness and strength within 120 min. Mechanical response to cyclical strains suggested viscoelasticity is due to two independent, self-recovering Ca(2+)-crosslinked networks. The networks display distinct pH dependence. The first network is attributed to Ca(2+)-stabilized phosphoserine motifs in H-fibroin, the second to Ca(2+) complexed carboxylate groups in the N-terminus of H-fibroin and a PEVK-like protein. These assignments were corroborated by IR spectroscopy. The results are consolidated into a multi-network model in which reversible rupture of the Ca(2+)-crosslinked domains at a critical stress results in pseudo-plastic deformation. Slow refolding of the domains results in nearly full recovery of fiber length, stiffness, and strength. The fiber toughening, energy dissipation, and recovery mechanisms, are highly adaptive for the high energy aquatic environment of caddisfly larvae.

Peroxinectin catalyzed dityrosine crosslinking in the adhesive underwater silk of a casemaker caddisfly larvae, Hysperophylax occidentalis

Aquatic caddisfly larvae use sticky silk fibers as an adhesive tape to construct protective composite structures under water. Three new silk fiber components were identified by transcriptome and proteome analysis of the silk gland: a heme-peroxidase in the peroxinectin (Pxt) sub-family, a superoxide dismutase 3 (SOD3) that generates the H2O2 substrate of the silk fiber Pxt from environmental reactive oxygen species (eROS), and a novel structural component with sequence similarity to the elastic PEVK region of the muscle protein, titin. All three proteins are co-drawn with fibroins to form silk fibers. The Pxt and SOD3 enzymes retain activity in drawn fibers. In native fibers, Pxt activity and dityrosine crosslinks are co-localized at the boundary of a peripheral layer and the silk fiber core. To our knowledge, dityrosine crosslinks, heme peroxidase, and SOD3 activities have not been previously reported in an insect silk. The PEVK-like protein is homogeneously distributed throughout the fiber core. The results are consolidated into a model in which caddisfly silk Pxt-catalyzed dityrosine crosslinking occurs post-draw using H2O2 generated within the silk fibers by SOD3. The ROS substrate of caddisfly silk SOD3 occurs naturally in aquatic environments, from biotic and abiotic sources. The radially inhomogeneous dityrosine crosslinking and a potential titin-like PEVK protein network have important implications for the mechanical properties of caddifly silk fibers.

Reversible assembly of β-sheet nanocrystals within caddisfly silk

Nuclear magnetic resonance (NMR) and X-ray diffraction (XRD) experiments reveal the structural importance of divalent cation-phosphate complexes in the formation of β-sheet nanocrystals from phosphorylated serine-rich regions within aquatic silk from caddisfly larvae of the species Hesperophyla consimilis. Wide angle XRD data on native caddisfly silk show that the silk contains a significant crystalline component with a repetitive orthorhombic unit cell aligned along the fiber axis with dimensions of 5.9 Å × 23.2 Å × 17.3 Å. These nanocrystalline domains depend on multivalent cations, which can be removed through chelation with ethylenediaminetetraacetic acid (EDTA). A comparison of wide angle X-ray diffraction data before and after EDTA treatment reveals that the integrated peak area of reflections corresponding to the nanocrystalline regions decreases by 15-25% while that of the amorphous background reflections increases by 20%, indicating a partial loss of crystallinity. (31)P solid-state NMR data on native caddisfly silk also show that the phosphorylated serine-rich motifs transform from a rigid environment to one that is highly mobile and water-solvated after treatment with EDTA. The removal of divalent cations through exchange and chelation has therefore caused a collapse of the β-sheet structure. However, NMR results show that the rigid phosphorus environment is mostly recovered after the silk is re-treated with calcium. The (31)P spin-lattice (T1) relaxation times were measured at 7.6 ± 3.1 and 1 ± 0.5 s for this calcium-recovered sample and the native silk sample, respectively. The shorter (31)P T1 relaxation times measured for the native silk sample are attributed to the presence of paramagnetic iron that is stripped away during EDTA chelation treatment and replaced with diamagnetic calcium.

Self-tensioning aquatic caddisfly silk: Ca2+-dependent structure, strength, and load cycle hysteresis

Caddisflies are aquatic relatives of silk-spinning terrestrial moths and butterflies. Casemaker larvae spin adhesive silk fibers for underwater construction of protective composite cases. The central region of Hesperophylax sp. H-fibroin contains a repeating pattern of three conserved subrepeats, all of which contain one or more (SX)n motifs with extensively phosphorylated serines. Native silk fibers were highly extensible and displayed a distinct yield point, force plateau, and load cycle hysteresis. FTIR spectroscopy of native silk showed a conformational mix of random coil, β-sheet, and turns. Exchanging multivalent ions with Na(+) EDTA disrupted fiber mechanics, shifted the secondary structure ratios from antiparallel β-sheet toward random coil and turns, and caused the fibers to shorten, swell in diameter, and disrupted fiber birefringence. The EDTA effects were reversed by restoring Ca(2+). Molecular dynamic simulations provided theoretical support for a hypothetical structure in which the (pSX)n motifs may assemble into two- and three-stranded, Ca(2+)-stabilized β-sheets.

β-Sheet nanocrystalline domains formed from phosphorylated serine-rich motifs in caddisfly larval silk: a solid state NMR and XRD study

Adhesive silks spun by aquatic caddisfly (order Trichoptera) larvae are used to build both intricate protective shelters and food harvesting nets underwater. In this study, we use (13)C and (31)P solid-state NMR and wide angle X-ray diffraction (WAXD) as tools to elucidate molecular protein structure of caddisfly larval silk from the species Hesperophylax consimilis . Caddisfly larval silk is a fibroin protein based biopolymer containing mostly repetitive amino acid motifs. NMR and X-ray results provide strong supporting evidence for a structural model in which phosphorylated serine repeats (pSX)4 complex with divalent cations Ca(2+) and Mg(2+) to form rigid nanocrystalline β-sheet structures in caddisfly silk. (13)C NMR data suggests that both phosphorylated serine and neighboring valine residues exist in a β-sheet conformation while glycine and leucine residues common in GGX repeats likely reside in random coil conformations. Additionally, (31)P chemical shift anisotropy (CSA) analysis indicates that the phosphates on phosphoserine residues are doubly ionized, and are charge-stabilized by divalent cations. Positively charged arginine side chains also likely play a role in charge stabilization. Finally, WAXD results finds that the silk is at least 7-8% crystalline, with β-sheet interplane spacings of 3.7 and 4.5 Å.

Fetal membrane patch and biomimetic adhesive coacervates as a sealant for fetoscopic defects

Iatrogenic preterm premature rupture of membranes after fetoscopic procedures affects 10-47% of patients, secondary to the non-healing nature of membranes and the separation of layers during the entry. In this study we developed an in vitro model to mimic the uterine wall-fetal membrane interface using a water column with one end sealed with human fetal membranes and poultry breast, and a defect was created with an 11 French trocar. Further, a fetal membrane patch in conjunction with multiphase adhesive coacervates modeled after the sandcastle worm bioadhesive was tested for sealing of an iatrogenic defect. The sealant withstood an additional traction of 12 g for 30-60 min and turbulence of the water column without leakage of fluid or slippage. The adhesive is non-toxic when in direct contact with human fetal membranes in an organ culture setting. A fetal membrane patch with multiphase adhesive complex coacervates may help to seal the defect and prevent iatrogenic preterm premature rupture of the membranes.

Localization of the bioadhesive precursors of the sandcastle worm, Phragmatopoma californica (Fewkes)

The marine sandcastle worm bonds mineral particles together into underwater composite dwellings with a proteinaceous glue. The products of at least four distinct secretory cell types are co-secreted from the building organ to form the glue. Prominent hetereogeneous granules contain dense sub-granules of Mg and the (polyphospho)proteins Pc3A and B, as well as at least two polybasic proteins, Pc1 and Pc4, as revealed by immunolabeling with specific antibodies against synthetic peptides. Equally prominent homogeneous granules comprise at least two polybasic proteins, Pc2 and Pc5, localized by immunolabeling with anti-synthetic peptide antibodies. The components of the sub-micrometer granule types are unknown, though positive staining with a redox-sensitive dye suggests the contents include o-dihydroxy-phenylalanine (dopa). Quantitative PCR and in situ hybridization demonstrated that a tyrosinase-like enzyme with a signal peptide was highly expressed in both the heterogeneous and homogeneous granules. The contents of the granules are poorly mixed in the secreted mixture that forms the glue. Subsequent covalent cross-linking of the glue may be catalyzed by the co-secreted tyrosinase. The first three parapodia of the sandcastle worm also contain at least two distinct secretory tissues. The Pc4 protein was immunolocalized to the anterior secretory cells and the tryosinase-like gene was expressed in the posterior secretory cells, which suggests these proteins may have multiple roles.

Modelling ultrasound-induced mild hyperthermia of hyperplasia in vascular grafts

BACKGROUND

Expanded polytetrafluoroethylene (ePTFE) vascular grafts frequently develop occlusive neointimal hyperplasia as a result of myofibroblast over-growth, leading to graft failure. ePTFE exhibits higher ultrasound attenuation than native soft tissues. We modelled the selective absorption of ultrasound by ePTFE, and explored the feasibility of preventing hyperplasia in ePTFE grafts by ultrasound heating. Specifically, we simulated the temperature profiles of implanted grafts and nearby soft tissues and blood under ultrasound exposure. The goal was to determine whether ultrasound exposure of an ePTFE graft can generate temperatures sufficient to prevent cell growth on the graft without damaging nearby soft tissues and blood.

METHODS

Ultrasound beams from two transducers (1.5 and 3.2 MHz) were simulated in two graft/tissue models, with and without an intra-graft cellular layer mimicking hyperplasia, using the finite-difference time-domain (FDTD) method. The resulting power deposition patterns were used as a heat source for the Pennes bioheat equation in a COMSOL(®) Multiphysics heat transfer model. 50°C is known to cause cell death and therefore the transducer powers were adjusted to produce a 13°C temperature rise from 37°C in the ePTFE.

RESULTS

Simulations showed that both the frequency of the transducers and the presence of hyperplasia significantly affect the power deposition patterns and subsequent temperature profiles on the grafts and nearby tissues. While neither transducer significantly raised the temperature of the blood, the 1.5-MHz transducer was less focused and heated larger volumes of the graft and nearby soft tissues than the 3.2-MHz transducer. The presence of hyperplasia had little effect on the blood's temperature, but further increased the temperature of the graft and nearby soft tissues in response to either transducer. Skin cooling and blood flow play a significant role in preventing overheating of the native tissues.

CONCLUSIONS

Modelling shows that ultrasound can selectively heat ePTFE grafts and produce temperatures that cause cell death on the graft. The temperature increase in blood is negligible and that in the adjacent soft tissues may be minimized by skin cooling and using appropriate transducers. Therefore, ultrasound heating may have the potential to reduce neointimal hyperplasia and failure of ePTFE vascular grafts.

Silk tape nanostructure and silk gland anatomy of trichoptera

Caddisflys (order Trichoptera) construct elaborate protective shelters and food harvesting nets with underwater adhesive silk. The silk fiber resembles a nanostructured tape composed of thousands of nanofibrils (∼ 120 nm) oriented with the major axis of the fiber, which in turn are composed of spherical subunits. Weaker lateral interactions between nanofibrils allow the fiber to conform to surface topography and increase contact area. Highly phosphorylated (pSX)(4) motifs in H-fibroin blocks of positively charged basic residues are conserved across all three suborders of Trichoptera. Electrostatic interactions between the oppositely charged motifs could drive liquid-liquid phase separation of silk fiber precursors into a complex coacervates mesophase. Accessibility of phosphoserine to an anti-phosphoserine antibody is lower in the lumen of the silk gland storage region compared to the nascent fiber formed in the anterior conducting channel. The phosphorylated motifs may serve as a marker for the structural reorganization of the silk precursor mesophase into strongly refringent fibers. The structural change occurring at the transition into the conducting channel makes this region of special interest. Fiber formation from polyampholytic silk proteins in Trichoptera may suggest a new approach to create synthetic silk analogs from water-soluble precursors.

Complex coacervates as a foundation for synthetic underwater adhesives

Complex coacervation was proposed to play a role in the formation of the underwater bioadhesive of the Sandcastle worm (Phragmatopoma californica) based on the polyacidic and polybasic nature of the glue proteins and the balance of opposite charges at physiological pH. Morphological studies of the secretory system suggested that the natural process does not involve complex coacervation as commonly defined. The distinction may not be important because electrostatic interactions likely play an important role in the formation of the sandcastle glue. Complex coacervation has also been invoked in the formation of adhesive underwater silk fibers of caddisfly larvae and the adhesive plaques of mussels. A process similar to complex coacervation, that is, condensation and dehydration of biopolyelectrolytes through electrostatic associations, seems plausible for the caddisfly silk. This much is clear, the sandcastle glue complex coacervation model provided a valuable blueprint for the synthesis of a biomimetic, water-borne, underwater adhesive with demonstrated potential for repair of wet tissue.

Natural Underwater Adhesives

The general topic of this review is protein-based underwater adhesives produced by aquatic organisms. The focus is on mechanisms of interfacial adhesion to native surfaces and controlled underwater solidification of natural water-borne adhesives. Four genera that exemplify the broad range of function, general mechanistic features, and unique adaptations are discussed in detail: blue mussels, acorn barnacles, sandcastle worms, and freshwater caddisfly larva. Aquatic surfaces in nature are charged and in equilibrium with their environment, populated by an electrical double layer of ions as well as adsorbed natural polyelectrolytes and microbial biofilms. Surface adsorption of underwater bioadhesives likely occurs by exchange of surface bound ligands by amino acid sidechains, driven primarily by relative affinities and effective concentrations of polymeric functional groups. Most aquatic organisms exploit modified amino acid sidechains, in particular phosphorylated serines and hydroxylated tyrosines (dopa), with high-surface affinity that form coordinative surface complexes. After delivery to the surfaces as a fluid, permanent natural adhesives solidify to bear sustained loads. Mussel plaques are assembled in a manner superficially reminiscent of in vitro layer-by-layer strategies, with sequentially delivered layers associated through Fe(dopa)(3) coordination bonds. The adhesives of sandcastle worms, caddisfly larva, and barnacles may be delivered in a form somewhat similar to in vitro complex coacervation. Marine adhesives are secreted, or excreted, into seawater that has a significantly higher pH and ionic strength than the internal environment. Empirical evidence suggests these environment triggers could provide minimalistic, fail-safe timing mechanisms to prevent premature solidification (insolubilization) of the glue within the secretory system, yet allow rapid solidification after secretion. Underwater bioadhesives are further strengthened by secondary covalent curing.

Enzymatic triggered release of an HIV-1 entry inhibitor from prostate specific antigen degradable microparticles

This paper describes the design, construction and characterization of the first anti-HIV drug delivery system that is triggered to release its contents in the presence of human semen. Microgel particles were synthesized with a crosslinker containing a peptide substrate for the seminal serine protease prostate specific antigen (PSA) and were loaded with the HIV-1 entry inhibitor sodium poly(styrene-4-sulfonate) (pSS). The particles were composed of N-2-hydroxyproplymethacrylamide and bis-methacrylamide functionalized peptides based on the PSA substrates GISSFYSSK and GISSQYSSK. Exposure to human seminal plasma (HSP) degraded the microgel network and triggered the release of the entrapped antiviral polymer. Particles with the crosslinker composed of the substrate GISSFYSSK showed 17 times faster degradation in seminal plasma than that of the crosslinker composed of GISSQYSSK. The microgel particles containing 1 mol% GISSFYSSK peptide crosslinker showed complete degradation in 30 h in the presence of HSP at 37°C and pSS released from the microgels within 30 min reached a concentration of 10 μg/mL, equivalent to the published IC(90) for pSS. The released pSS inactivated HIV-1 in the presence of HSP. The solid phase synthesis of the crosslinkers, preparation of the particles by inverse microemulsion polymerization, HSP-triggered release of pSS and inactivation of HIV-1 studies are described.

Multiphase adhesive coacervates inspired by the Sandcastle worm

Water-borne, underwater adhesives were created by complex coacervation of synthetic copolyelectrolytes that mimic the proteins of the natural underwater adhesive of the sandcastle worm. To increase bond strengths, we created a second polymer network within cross-linked coacervate network by entrapping polyethylene glycol diacrylate (PEG-dA) monomers in the coacervate phase. Simultaneous polymerization of PEG-dA and cross-linking of the coacervate network resulted in maximum shear bond strengths of ∼1.2 MPa. Approximately 40% of the entrapped PEG-dA polymerized based on attenuated total reflectance-Fourier transform infrared spectroscopy. The monomer-filled coacervate had complex flow behavior, thickening at low shear rates and then thinning suddenly with a 16-fold drop in viscosity at shear rates near 6 s(-1). The microscale structure of the complex coacervates resembled a three-dimensional porous network of interconnected tubules. The sharp shear thinning behavior is conceptualized as a structural reorganization between the interspersed phases of the complex coacervate. The bond strength and complex fluid behavior of the monomer-filled coacervates have important implications for medical applications of the adhesives.

Bidirectional power stroke by ncd kinesin

Optical trapping experiments reveal details of molecular motor dynamics. In noisy data, temporal structure within the power stroke of motors can be analyzed by ensemble averaging, but this obscures infrequent subcategories of events. We have here developed an analysis method that uses Kalman filtering of measurements, model-based estimation of the power strokes produced by the motor head, and automatic event classification to discriminate between different types of motor events. This method was applied to optical trap measurements of power strokes of the Drosophila kinesin-14 ncd in a three-bead geometry. We found the majority of events to be consistent with the previously discovered minus-end directed power stroke of ncd, occurring with ATP binding. Unexpectedly, 30% of apparent power strokes were plus-directed and 6% of binding events did not terminate in a discernible stroke. Ensemble averaging for each event category revealed that plus- and minus-directed strokes have different size and occur at different instants within the ncd-MT attachment sequence.

Controlled curing of adhesive complex coacervates with reversible periodate carbohydrate complexes

Periodate oxidation of carbohydrates with vicinal hydroxyl groups and aromatic ortho-dihydroxyphenyl groups has been employed extensively to initiate crosslinking or conjugation reactions in adhesive biomaterials. Periodate forms stable tridentate complexes with carbohydrates containing three appropriately configured hydroxyls, such as 1,2-O-isopropylidene-a-D-glucofuranose, that are not appreciably oxidized relative to carbohydrates with vicinal hydroxyls and ortho-dihydroxyphenyl groups. In the presence of 1,2-O-Isopropylidene-a-D-glucofuranose the rate of periodate oxidation of dihydroxy containing compounds is controlled by the rates of association and dissociation of the periodate-carbohydrate complex. By varying the ratio of 1,2-O-isopropylidene-a-D-glucofuranose to periodate the curing rate of adhesive complex coacervates was varied over a wide range.

Biocompatibility of adhesive complex coacervates modeled after the sandcastle glue of Phragmatopoma californica for craniofacial reconstruction

Craniofacial reconstruction would benefit from a degradable adhesive capable of holding bone fragments in three-dimensional alignment and gradually being replaced by new bone without loss of alignment or volume changes. Modeled after a natural adhesive secreted by the sandcastle worm, we studied the biocompatibility of adhesive complex coacervates in vitro and in vivo with two different rat calvarial models. We found that the adhesive was non-cytotoxic and supported the attachment, spreading, and migration of a commonly used osteoblastic cell line over the course of several days. In animal studies we found that the adhesive was capable of maintaining three-dimensional bone alignment in freely moving rats over a 12 week indwelling period. Histological evidence indicated that the adhesive was gradually resorbed and replaced by new bone that became lamellar across the defect without loss of alignment, changes in volume, or changes in the adjacent uninjured bone. The presence of inflammatory cells was consistent with what has been reported with other craniofacial fixation methods including metal plates, screws, tacks, calcium phosphate cements and cyanoacrylate adhesives. Collectively, the results suggest that the new bioadhesive formulation is degradable, osteoconductive and appears suitable for use in the reconstruction of craniofacial fractures.

Adaptation of caddisfly larval silks to aquatic habitats by phosphorylation of h-fibroin serines

Aquatic caddisflies diverged from a silk-spinning ancestor shared with terrestrial moths and butterflies. Caddisfly larva spin adhesive silk underwater to construct protective shelters with adventitiously gathered materials. A repeating (SX)(n) motif conserved in the H-fibroin of several caddisfly species is densely phosphorylated. In total, more than half of the serines in caddisfly silk may be phosphorylated. Major molecular adaptations allowing underwater spinning of an ancestral dry silk appear to have been phosphorylation of serines and the accumulation of basic residues in the silk proteins. The amphoteric nature of the silk proteins could contribute to silk fiber assembly through electrostatic association of phosphorylated blocks with arginine-rich blocks. The presence of Ca(2+) in the caddisfly larval silk proteins suggest phosphorylated serines could contribute to silk fiber periodic substructure through Ca(2+) crossbridging.